1. Field of the Invention
This invention relates to a non-contact power transmitting device for electrical equipment which is suitably employed in a battery charger, or a water facility such as a bath room.
2. Description of the Related Art
Heretofore, a non-contact power transmitting device is popularly employed in which a power supplying section having a power transmitting primary coil, and a load section having a power transmitting secondary coil are separately provided, and when the load section is attached to the power supplying section the primary coil and the secondary coil are magnetically coupled to each other, and power is transmitted from the self-oscillating power supplying section to the load section by electromagnetic induction. The non-contact power transmitting device is applied to electrical equipment employed especially in a water facility.
In such a non-contact power transmitting device, it is preferable that, when the load section is not attached to the power supplying section, the self-oscillation of the power supplying section is stopped, or the self-oscillation is weakened. This is because, if the self-oscillation is continued although the load section is no t attached to the power supplying section, then power loss occurs with the power supplying section; that is, energy loss is involved, and accordingly if a metal piece is arranged near the power supplying section, the metal piece is heated by induction heating action.
In order to overcome this difficulty, the following non-contact power transmitting device has been proposed in the art: In addition to the power transmitting coils, a pair of signaling coils are provided. When, with the load attached to the power supplying section, power is transmitted to the load section by the electromagnetic induction of a pair of power transmitting coils of the power supplying section and the load section, the power is employed to drive the control circuit of the load section. And a control signal outputted by the control circuit is returned from the load section to the power supplying section with the aid of the pair of signaling coils. The oscillation operation is controlled according to the control signal thus returned, thereby to detect the aimed load section (cf. Japanese Patent Publication No. Hei. 6-311658).
In the above-described device under Japanese Patent Publication No. Hei. 6-311658, it is necessary to additionally provide a circuit for detecting the load section, and a circuit for controlling the oscillation. Accordingly, its circuit is unavoidably intricate; that is, the device is high in manufacturing cost.
On the other hand, Japanese Patent Publication No. Hei. 6-1768464 has disclosed a non-contact power transmitting device of which circuitry is relatively simple. The device is to synchronously control the resonance frequency of the load section and the oscillation frequency of the power supplying section, and is applied to the case where the gap between the power supplying section and the load section. Accordingly, in the device, even if the load section is not attached to the power supplying section, the oscillation is continued in the power supplying section. Hence, the device is different from the one that the load section is detected to stop or weaken the oscillation.
As is apparent from the above description, there has been a strong demand for the provision of a non-contact power transmitting device in which, in the case where the load section is not attached to the power supplying section, a simple circuit stops or weakens the oscillation of the power supplying section.